Process and device for coating a finely milled solid

ABSTRACT

The present invention relates to a process for the application of a liquid to a finely milled solid, which process is characterized in that the liquid to be applied to the finely milled solid is introduced into the milling zone of a fine milling apparatus during the milling operation or simultaneously with the introduction of the material for milling, and the fine milling is carried out in the presence of the finely divided liquid, and to a device for carrying out this process.

The present invention relates to a process for the application ofliquids to finely milled solids and to a device for carrying out thisprocess.

The processing of finely milled solids charged with liquid is widespreadin many branches of industry, for example in the industrial manufactureand processing of foodstuffs, fine chemicals, pharmaceuticals or cropprotection products. The application of the liquid is intended toprovide the finely milled solid with particular properties which areadvantageous for the intended use.

It is known to apply liquids to finely milled solids as follows: thesolid is first finely milled, and the liquid that is to be applied isthen applied to the solid in a mixing device in the form of a finespray, followed by intensive mixing of the mixture thus obtained.

Using that process it is not possible to achieve a homogeneousdistribution of the liquid on the solid, because lumps form during themixing of the liquid with the finely milled solid, especially whenviscous liquids are being used. The resulting mixture must thereforeundergo at least one further milling process. The known process for theapplication of liquids to milled solids accordingly comprises thefollowing individual steps:

-   -   milling of the solid;    -   application of the liquid by spraying, and mixing of the milled        solid with the liquid; and    -   further milling and/or homogenisation of the resulting mixture,        one or more further milling operations being necessary,        depending on the type of liquid applied.

Not only is this process laborious, but in most cases, especially whenthe liquid to be applied is viscous, a homogeneous distribution of theliquid on the particles of the solid is not achieved, despite thesubsequent additional milling operation.

The object of the present invention is to provide a process for theapplication of a liquid to a finely milled solid, which process avoidsthe disadvantages of the prior art process and, in a simple manner,permits the production of finely milled solids whose particles arehomogeneously charged with a liquid.

According to the present invention it is proposed to achieve that objectas follows: the liquid to be applied to the finely milled solid isintroduced into the milling zone of a fine milling apparatus during themilling operation or simultaneously with the introduction of thematerial for milling, and the fine milling is carried out in thepresence of the finely divided liquid.

The process according to the invention can in principle be carried outusing any conventional fine milling apparatus if such an apparatus isprovided with a device which enables the liquid that is to be applied tothe finely milled solid to be introduced into the milling zone duringthe milling operation or simultaneously with the introduction of thematerial for milling. Especially suitable are mills, in which thematerial for milling is moved by a gas stream flowing through themilling zone, and which are provided with a device with which the finelydivided liquid is introduced into the milling zone simultaneously withthe introduction of the material for milling. Especially suitable millsare, for example, gas-jet mills or fluidised-bed counter-jet mills, inwhich the solid moved by the milling gas stream flowing at very highspeed is comminuted in the milling zone by the action of the impact ofthe particles of the solid. When that type of mill is used, the excesspressure of the milling gas introduced into the milling zone is in therange of from 5 bar to 10 bar, especially from 6 bar to 7 bar. Theexcess pressure of the liquid introduced into a gas stream flowingthrough the milling zone or directly into the milling zone is likewisein the range of from 5 bar to 10 bar, especially from 6 bar to 7 bar,but the excess pressure of the liquid is in each case from 0.25 bar to 1bar above the pressure of the milling gas.

The process according to the invention is preferably carried out atambient temperature. The temperature may, however, also be up to 50° C.,especially up to 30° C., below or above the ambient temperature,depending, for example, on the nature of the finely milled solid, on thepressure or on the temperature of the finely milled solid or of theliquid.

Gas-jet mills and fluidised-bed counter-jet mills are especiallysuitable for carrying out the process according to the Inventionbecause, apart from the particles of the solid moved by the milling gas,they comprise no mechanically moved parts. As a result, mechanicalignition sources are avoided, which constitutes a considerable advantagewhen processing combustible mixtures.

Further suitable fine milling apparatuses are mechanical mills, such asimpact mills or hammer mills, in which the material for milling is movedthrough the mill by means of a carrier gas and/or a mechanical feeddevice, such as a star wheel or a feed screw. In an impact mill, thesolid is comminuted against the impact surfaces arranged in the millingzone. In a hammer mill, the solid is comminuted by rotating hammers, andgas is preferably used as the carrier medium for the material formilling. The pressure of the carrier gas is generally in the region ofthe ambient pressure. Depending on the type of milling apparatus, thepressure may also be up to 0.3 bar below or above the ambient pressure.The liquid is sprayed into the milling apparatus with a pressure that isabove the pressure prevailing in the mill. Unitary or binary nozzles areespecially suitable for spraying in the liquid. When a unitary nozzle isused, the pressure is preferably in the range of from 4 bar to 10 bar.When a binary nozzle is used, the pressure is preferably in the range offrom 3 bar to 4 bar.

The process according to the invention is preferably also carried out atambient temperature when a mechanical mill is used. However, thetemperature may also be up to 50° C., especially up to 30° C., below orabove the ambient temperature, depending, for example, on the nature ofthe finely milled solid, on the pressure or on the temperature of thefinely milled solid or of the liquid.

As solids there come into consideration according to the invention allsolid organic or inorganic substances in pure form or in the form ofmixtures of different solids. The process according to the invention isespecially advantageous in the case of mixtures of solids, such as solidready-for-use formulations of pharmaceutical or agrochemical activeingredients or solid preparations of foodstuffs. For example, solidready-formulated crop protection products, such as solid acaricides,fungicides, growth regulators, herbicides, insecticides or nematocides,can be charged with a liquid in order to improve their in-useproperties, for example to achieve a better wetting of the plant or animprovement in the biological activity of the product or to facilitatethe preparation of a spray broth by an improved distribution behaviourof the product in water. The particle size (diameter) of the solids orsolid mixtures introduced into the mill as the material for fine millingis generally in the range of from 40 μm to 200 μm, preferably from 80 μmto 120 μm. After the completion of the fine milling operation, theparticle size (diameter) of the finely milled solid is generally in therange of from 1 μm to 10 μm, preferably from 2 μm to 4 μm.

The process according to the invention can also be used for thehomogeneous application of liquids to solids that are already in finelymilled form. The present invention relates also to this specificembodiment of the process.

The amount of the liquid to be applied is in the range of from 0.001% byweight to 20% by weight, especially from 0.01% by weight to 10% byweight, preferably from 0.5% by weight to 5% by weight, based on theamount of the solid.

When the process according to the invention is carried out in mills inwhich the material for milling is moved by a milling gas stream or by acarrier gas stream, air is generally used as the milling or carrier gas.When processing explosive or readily oxidisable materials, however, itis also possible to use an inert gas, especially nitrogen.

As liquids that can be applied by means of the process according to theinvention to finely milled solids there come into consideration, forexample, liquid active ingredients, solutions of active ingredients,surface-active substances, such as non-ionic, anionic or cationicsurfactants or detergents, flavourings and attractants, it beingpossible for surface-active substances, flavourings and attractants tobe used, according to their physical properties, in the form of thesubstances per se or in the form of solutions.

The present invention relates also to a device for carrying out theprocess according to the invention, which device, as well as comprisingmeans for introducing and for finely milling the material for millingand means for separating off and discharging the product, comprises adevice which enables a finely divided liquid to be metered into themilling zone during the fine milling operation or simultaneously withthe introduction of the material for milling. The device according tothe invention is preferably based on a mill through which there flows amilling or carrier gas, which mill, as well as comprising a millingzone, a pipe for supplying the material for milling to the milling zone,a pipe for supplying the milling or carrier gas to the milling zone, adischarge pipe for the milling or carrier gas containing the finelymilled solid charged with a liquid, and a separating device forseparating the finely milled solid charged with a liquid from themilling or carrier gas, comprises a device which enables a finelydivided liquid to be metered into the milling zone either by way of thecarrier gas stream or directly.

Examples of suitable devices for carrying out the process according tothe invention are shown in the FIGS. 1 (FIG. 1) and 2 (FIG. 2).

FIG. 1 shows, in diagrammatic form, a gas-jet or fluidised-bedcounter-jet mill which is provided according to the invention with adevice for introducing a liquid. The continuous lines show the standarddevice. Several of the possible alternative embodiments are shown bybroken lines.

FIG. 2 shows, in diagrammatic form, a mechanical mill which is providedaccording to the invention with a device for introducing a liquid. InFIG. 2 also, the continuous lines show the standard device, whileseveral of the possible alternative embodiments are shown by brokenlines.

The process according to the invention is explained hereinbelow withreference to the devices shown in the FIGS. 1 and 2.

FIG. 1

The material for milling is introduced into the gas-jet mill 101 fromthe storage container 102 via the feed device 103 and the pipe 105. Thematerial for milling is fed into the gas-jet mill by means of a millinggas stream which is supplied through the pipe 104. At the same time, theliquid that is to be applied to the finely milled solid is introduced,from the storage container 109 via the pipe 110 and the metering pump111, into the carrier gas supplied through the pipe 106. The liquid iseither supplied via the nozzle 112, or is supplied directly (not shownin FIG. 1), to the carrier gas stream flowing at very high speed. Thenozzle 112 is not absolutely necessary, because the liquid is atomisedin the carrier gas stream flowing at very high speed even without theuse of a nozzle (“Venturi effect”). The carrier gas/liquid mixture thusformed is introduced into the gas-jet mill 101 via the pipe 106 and thenozzle 107. The introduction of the carrier gas/liquid mixture into thegas-jet mill 101 can also take place using several nozzlessimultaneously. The ratio of solid to liquid is controlled by means ofthe regulating unit 118, which is connected to the metering pump 111 andthe feed device 103 by the control lines 119. The product/gas mixtureleaving the gas-jet mill 101 is supplied via the pipe 113 to theseparating device 114, from which the product separated from the gas isremoved via the pipe 115. The gas separated from the product isdischarged via the pipe 116. If desired, additional carrier gas can besupplied via the pipe 113 a to the pipe 113 containing the product/gasmixture, in order to support the carriage of the product/gas mixture tothe separating device 114. Instead of being introduced via the pipe 110(not shown in FIG. 1) or the nozzle 112 into the carrier gas suppliedthrough the pipe 106, the liquid can also be introduced directly intothe gas-jet mill 101 via the pipe 110 a and the liquid nozzle 108.Furthermore, it is possible, that the gas separated from the product isnot discharged from the device via the pipe 116 but is returned via thepipe 116 a and the compressor 117 into the pipe 106 for the carrier gas.This procedure is advisable especially when a gas other than air, e.g.nitrogen, is used. A portion of the gas returned through the pipe 116 acan also be introduced via the pipe 116 b into the pipe 104 and used asmilling gas. The supply of fresh gas, which is necessary owing to lossesof gas, can be effected via the pipe 104 and/or the pipe 106.

FIG. 2

The material for milling is introduced into the mechanical mill 201 fromthe storage container 202 via the feed device 203, for example a starwheel or a feed screw, and the pipe 204. At the same time, the liquidthat is to be applied to the finely milled solid is introduced, from thestorage container 208 via the pipe 209, the metering pump 210 and thenozzle 211, into the carrier gas supplied through the pipe 205. Thecarrier gas/liquid mixture thus formed is introduced into the mechanicalmill 201 via the pipe 205 and the nozzle 206. The introduction of thecarrier gas/liquid mixture into the mechanical mill 201 can also takeplace using several nozzles simultaneously. The ratio of solid to liquidis controlled by the regulating unit 217, which is connected to the feeddevice 203 and the metering pump 210 by the control lines 218. Theproduct/gas mixture leaving the mechanical mill 201 is supplied via thepipe 212 to the separating device 213, from which the product separatedfrom the gas is removed via the pipe 214. The gas separated from theproduct is discharged via the pipe 215. If desired, additional carriergas can be supplied via the pipe 212 a to the pipe 212 containing theproduct/gas mixture, in order to support the carriage of the product/gasmixture to the separating device 213. Instead of being introduced viathe nozzle 211 into the carrier gas supplied through the pipe 205, theliquid can also be introduced directly into the mechanical mill 201 viathe pipe 209 a and the liquid nozzle 207. Furthermore, it is possible,that the gas separated from the product is not discharged from thedevice via the pipe 215 but is returned via the pipe 215 a and thecompressor 216 into the pipe 205 for the carrier gas. This procedure isadvisable especially when a gas other than air, e.g. nitrogen, is used.The supply of fresh gas, which is necessary owing to losses of gas, canbe effected via the pipe 205.

The process according to the invention for the production of finelymilled solids charged with a liquid has, for example, the followingadvantages over the known process:

-   -   The process according to the invention constitutes a substantial        simplification, because it enables the solid to be finely milled        and the finely milled solid to be charged with a liquid in a        single operation, while at least three operations are required        with the known process.    -   The process according to the invention permits a homogeneous        distribution of the liquid on the particles of the finely milled        solid and accordingly a substantially better product quality.    -   It is possible using the process according to the invention for        even very small amounts of highly viscous liquids to be applied        homogeneously to the particles of the finely milled solid in a        simple manner, which with the known process is possible only        with a considerable outlay or is not possible at all.    -   The process according to the invention, especially when carried        out in gas-jet mills or fluidised-bed counter-jet mills, offers        an increased safety in the processing of combustible solids or        mixtures of solids, because in gas-jet mills or fluidised-bed        counter-jet mills, in contrast to the mixers used in accordance        with the prior art, there are no mechanically moved machine        parts which can act as sources of ignition.

The following Examples explain the present invention in greater detail.Neither these Examples nor the Examples shown in the FIGS. 1 and 2constitute a limitation of the present invention.

EXAMPLES Example 1

A water dispersible powder for slurry seed treatment (WS formulation),which comprises as active ingredient the insecticidal compoundthiamethoxam in an amount of 70% by weight, is prepared. The solid rawmaterial, consisting of the insecticidally active ingredient andcustomary auxiliaries and adjuvants, which has a mean particle size(diameter) of about 100 μm, is fed into a gas-jet mill according toFIG. 1. Air is used as the milling gas and the carrier gas. A highlyviscous polyoxyethylene-polyoxypropylene copolymer liquid, heated to 50°C., having a dynamic viscosity of >4000 mPas, is added to the carriergas stream in an amount of 4.5% by weight, based on the amount of thesolid raw material fed in. The excess pressure is 6 bar in the millinggas stream and 6.5 bar in the carrier gas/liquid stream. In theresulting product, which exhibits improved handling properties, 50% ofthe milled particles have a particle size (diameter) of less than 3.7 μmand 90% of the milled particles have a particle size (diameter) of lessthan 11.1 μm, the liquid being homogeneously distributed on theparticles of the finely milled solid.

The product thus obtainable exhibits a homogeneous distribution of theliquid on the particles of the finely milled solid, which cannot beobtained using the process of the prior art.

This difference in the homogeneities of the products is shown in theFIGS. 3 and 4, FIG. 3 illustrating the product quality achievable by theprior art process, i.e. by finely milling the solid, adding to thefinely milled solid the liquid to be applied, mixing, further millingand mixing again, and FIG. 4 illustrating the homogeneity achievable bythe process according to the invention.

Not only exhibits the product thus obtainable a substantially betterquality, but the process for its preparation also constitutes, comparedwith the known process, a substantial simplification. At the same time,the risk of a powder explosion is markedly reduced, because according tothe exemplified process there are no mechanically moved machine parts,which could come into contact with the product and act as sources ofignition.

Example 2

In a manner analogous to that described in Example 1 the productobtainable according to the process of Example 1 can also be preparedusing an inert milling gas, such as nitrogen or argon.

1. A process of applying a liquid to a finely milled solid, in which theliquid to be applied to a solid that is to be finely milled isintroduced into the milling zone of a fine milling device during themilling operation or simultaneously with the introduction of the solidto be finely milled, and the fine milling is carried out in the presenceof the finely divided liquid.
 2. A process according to claim 1, inwhich there is used a fine milling device in which the material formilling is moved by a gas stream flowing through the milling zone.
 3. Aprocess according to claim 1, in which a gas-jet or fluidised-bedcounter-jet mill is used.
 4. A process according to claim 1, in which animpact mill is used.
 5. A process according to claim 1, in which ahammer mill is used.
 6. A process according to claim 1, in which aready-formulated active ingredient mixture is used as the solid to befinely milled and charged with a liquid.
 7. A process according to claim1, in which a ready-formulated pesticide or a crop protection product isused as the material for milling.
 8. A process according to claim 1, inwhich the particle size of the solid to be finely milled is in the rangeof from 40 μm to 200 μm.
 9. A process according to claim 1, in which theparticle size of the solid to be finely milled is in the range of from80 μm to 120 μm.
 10. A process according to claim 1, in which the liquidto be applied to the finely milled solid is a liquid active ingredient,the solution of an active ingredient, a surface-active substance, aflavouring or an attractant.
 11. A process according to claim 1, inwhich the amount of liquid to be applied is in the range of from 0.01 to10% by weight, based on solid to be finely milled.
 12. A device forcarrying out the process according to claim 1, which device, as well ascomprising means for introducing and for finely milling the material tobe milled and means for discharging the product, comprises a devicewhich enables a finely divided liquid to be metered into the millingzone during the fine milling operation or simultaneously with theintroduction of the material for milling.
 13. A device according toclaim 12, through which a milling or carrier gas flows and which, aswell as comprising a milling zone, a pipe for supplying the material formilling to the milling zone, a pipe for supplying the milling or carriergas to the milling zone, a discharge pipe for the milling or carrier gascontaining the finely milled solid charged with a liquid, and aseparating device for separating the finely milled solid charged with aliquid from the milling or carrier gas, comprises a device which enablesa finely divided liquid either to be metered into the milling zone byway of the milling or carrier gas stream or to be metered directly intothe milling zone.
 14. A device according to claim 12, comprising agas-jet mill 101, a storage container 102 for the material for milling,a feed device 103 for the material for milling, which feed device 103 isprovided with a supply pipe 104 for carrier gas, a supply pipe 105 forintroducing the material for milling into the gas-jet mill 101, a supplypipe 106 for the milling gas, a discharge pipe 113 for the milling gascontaining the finely milled solid charged with a liquid, a device 114for separating the finely milled solid charged with a liquid from themilling gas, a pipe 115 for removing the finely milled solid chargedwith a liquid, and a discharge pipe 116 for the milling gas freed of thesolid, which device is provided with a storage container 109 for theliquid to be applied, a pipe 110 for supplying the liquid to be appliedinto the milling gas stream 106, a liquid pump 111, arranged in thesupply pipe 110, for metering the liquid either into the milling gasstream 106 or via pipe 110 a and a nozzle 108 into the gas-jet mill 101,and a regulating device 118, which is connected to the pump 111 and thefeed device 103 via a control line 119, for controlling the ratio ofsolid to be finely milled to liquid to be applied.
 15. A deviceaccording to claim 14, which, instead of being provided with a pipe 116for discharging the milling gas freed of the finely milled solid, isprovided with a pipe 116 a for returning the milling gas freed of thesolid into the supply pipe 106 and with a compressor 117 arranged in thepipe 116 a.
 16. A device according to claim 12, comprising a mechanicalmill 201, a storage container 202 for the material for milling, a feeddevice 203 for the material for milling, a supply pipe 204 forintroducing the material for milling into the mechanical mill 201, asupply pipe 205 for the carrier gas, a discharge pipe 212 for thecarrier gas containing the finely milled solid charged with a liquid, adevice 213 for separating the finely milled solid charged with a liquidfrom the carrier gas, a pipe 214 for removing the finely milled solidcharged with a liquid, and a discharge pipe 215 for the carrier gasfreed of the solid, which device is provided with a storage container208 for the liquid to be applied, a supply pipe 209 for the liquid to beapplied, a liquid pump 210, arranged in the supply pipe 209, formetering the liquid either into the carrier gas stream 205 or via pipe209 a and a nozzle 207 into the mechanical mill 201, and a regulatingdevice 217, connected to the pump 210 and the feed device 203 via acontrol line 218, for controlling the ratio of solid to be finely milledto liquid to be applied thereto.
 17. A device according to claim 16,which, instead of being provided with a pipe 215 for discharging themilling gas freed of the finely milled solid, is provided with a pipe215 a for returning the milling gas freed of the solid into the supplypipe 205 and with a compressor 216 arranged in the pipe 215 a.
 18. Adevice according to claim 14, in which the liquid container 109 or 208,the pipe 110 or 209 and the pump 111 or 210 is provided with a heatingdevice.